A large size liquid crystal panel is utilized as a display device for amusement facilities, an information display, a digital signage, or the like. With the increase in variety of uses, it is tried to artificially realize a large screen display device by arranging a plurality of liquid crystal panels (sometimes referred to as a tiling technique). Such configuration is referred to as a multi display system or the like, and is paid attention to as a system for realizing a large screen with high definition.
However, in the multi display system, there occurs a problem that joints between a plurality of display panels are relatively noticeable. The problem will be described by way of an example of a liquid crystal display device.
A liquid crystal display device includes a liquid crystal display panel, a backlight unit, circuits for supplying various electrical signals to the liquid crystal display panel, a power supply, and a housing for accommodating them. The liquid crystal display panel has a display area in which a plurality of pixels are arranged, and a frame area around the display area.
The display area (an active area) is provided with pixel electrodes, TFTs, and the like, thereby displaying images, videos, and the like. On the other hand, the frame area is provided with a sealing portion for sticking substrates together so as to enclose liquid crystal materials between the substrates, wirings connected to gate electrodes and source electrodes of the TFTs, terminals for the connection to external driving circuits for inputting signals/scanning voltages, and the like. In order to prevent light leakage from the backlight, and to prevent the degradation of display quality in an outer circumferential portion of the active area caused by the disorder of alignment of liquid crystal molecules, a black mask (a light shielding member) is usually provided in the frame area. As described above, the frame area is an area which does not contribute to the display (an invalid display portion). The technique for narrowing the frame area of the liquid crystal display device is advanced year after year, but it is impossible to eliminate the frame area in principle.
In the multi display system, neighboring display panels are joined (coupled) on the outer edge side of bezels. Such a portion in which the bezel is disposed is also the invalid display portion. The region which does not contribute to the display around the active area is observed as a black frame between panel modules in the multi-panel configuration. For example, in the case where an image including a large object expanding over a plurality of panels is to be displayed, it is disadvantageously felt that the image quality of the entire multi-panel configuration is degraded due to the black frame.
In the multi display configuration utilizing a plurality of display panels, various methods for making the joints of the panel boundary portions less noticeable have been studied. For example, Patent Document No. 1 discloses, in order to display an image in which the joints are less noticeable on the whole multi panel display device, a configuration in which a translucent cover is provided on the observer side of the respective display panels.
A curved surface is formed in an edge portion on the observer side of the translucent cover. The curved surface portion functions as a lens. The curved surface portion (the lens portion) of the translucent cover is provided so as to cover the frame area of the display panel and a portion of the display area (a peripheral display area). The light emitted from pixels arranged in the peripheral display area is refracted in the lens portion. As a result, the image is observed so as to be displayed on part of the frame area. Accordingly, an image in which the joints are less noticeable can be displayed over the whole screen.
A method in which a projector is utilized, so as to perform display by combining a plurality of projected images is known in the technical field of VR (virtual reality) video technologies or the like. Patent Document No. 2 describes a projector which can obtain a screen with less noticeable boundary of divided images by superimposing a projected image on a portion corresponding to the joint of the divided images and by adjusting the luminance of the superimposed portion. As described above, in an end portion of the divided image, image signal processing which is different from that in the other portion is considered to be effective means. In this specification, in the multi display system, the image/picture displayed on each display panel is sometimes referred to as a divided image.
Patent Document No. 3 discloses a technique for making the joint of liquid crystal panels less noticeable by disposing a cylindrical lens between a light source and the panels in a position in the vicinity of the joint. In the display device described in Patent Document No. 3, the light from the light source is incident on an outermost edge portion of the liquid crystal panel via the cylindrical lens. The light passes through the pixels in the outermost edge portion, and thereafter reaches both sides of the position corresponding to the joint portion on the front panel, thereby forming a region with high luminance. In this way, a black rim or a black lattice pattern caused by the joint portion is made to be less noticeable.
In addition, Patent Document No. 4 shows a configuration in which a Fresnel lens is provided so as to cover the entire panel on the observer side of plasma display panels disposed adjacently. Herein, by means of the Fresnel lens, the projected images from the respective panels are displayed in an enlarged manner at the front of the respective panels. Accordingly, the observer can see the image as if the image also exists in the position corresponding to the joint of the panels.